Billion 7404 router, open UDP 7070 port

This routers default has port 7070 open to incoming and outgoing traffic. 7070 is Automatic Router Control Protocol.
I have blocked this open incoming port and still have a functional internet connection.
Is this port required by the ISP’s hardware to control my router?

I have since found this link
RealNetworks RealSystem Firewall Support
and can understand why RealPayer needs port7070 open, but not why Billion router defaults to open incoming port 7070 ?

It may be to allow your isp to manage configuration of your modem’s firewall software - your best source of information would be your isp’s tech support.